class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("输入一个学生成绩：");
        int a=Convert.ToInt32(Console.ReadLine());
        if (a > 100 || a < 0)
            Console.WriteLine("输入错误");
        else
        {
            if (a >= 90)
                Console.WriteLine("A");
            else if(a>=60&&a<=89)
                Console.WriteLine("B");
            else if(a<60)
                Console.WriteLine("C");
        }
        Console.ReadKey();
    }
}